Switchgear is an essential equipment in circuit which plays switching on and switching off function in the circuit. While switching off, switchgear has very high resistance in order to withstand certain voltage; While switching on, it must have very low resistance in order to pass rated current without overheat. During switchgear contacts interrupting, arc extinguishing is necessary to make contacts to be quickly separated. At present, there are different kinds of arc extinguishing medium: oil, sulphur hexafluride (SF6), air, semiconductor and vacuum etc. Different arc extinguishing mediums correspond to different interrupter structures and with different properties. As vacuum interrupter has small gap, high withstand voltage, low arc voltage, high current interrupting capability, low electrode erosion and high electric life, so it is broadly used in power line under 35 KV voltage. As shown in FIG. 1, the heart of a vacuum interrupter 7 is its vacuum arc extinguished chamber 6 within envelope 5. The properties of contacts 1 and 2 within vacuum arc extinguished chamber 6 determine properties of vacuum interrupter 7 directly. The rear of contacts 1 and 2 of vacuum interrupter 7 is connected to moving electrode 3 and stationary electrode 4, respectively, interruption of contacts 1 and 2 is mechanically operated by moving electrode 3. During interruption, contact area of contacts 1 and 2 is getting smaller until there is only one contact point between contacts 1 and 2. At the same time, contact resistance and area temperature are increased until the contact point is melted, vaporized and ionized. Metal vapor keeps discharge procedure to be continued in vacuum and produces vacuum arc, finally contacts are electrically interrupted. In order to raise interrupting capability of vacuum interrupter, it is necessary to provide vacuum arc with axial magnetic field, which maintains vacuum arc at a stable and dispersive state. In this way, current will be well distributed on contact surface, temperature on contact surface will be decreased and amount of vaporization of contact material is avoided, all of these maintaining arc voltage at a lower level and decreasing electrical erosion of contact. Therefore, contacts in arc extinguished chamber of vacuum interrupter must have abilities of burning arc, conducting electrically and producing magnetic field. Its technical parameters need to satisfy following requirements: excellent anti-welding characteristics, excellent voltage withstanding characteristics, high current-interrupting capability, excellent anti-electric erosion characteristics, low current chopping characteristics, low air content, high conductivity, small geometric size and high reliability etc. Currently, the contact consists of an arc proof component, a conductive component and a magnetic field generating component. As shown in FIG. 2, the arc proof component 11 is set in the middle part and consists of copper-chromium (CuCr) material, which has large current interrupting capability and excellent anti-welding characteristics and produces metal vapor during interrupting time to maintain current. The conductive component 12 is a round contact body and is generally made of copper material. The magnetic field generating component 13 is an inductance coil and set outside of the contact body; whether at an axial magnetic field or at a radial magnetic field, its magnetic field intensity is comparatively low. When assembled, it is necessary to solder in a vacuum and heating furnace with silver copper solder to combine the components together. As every component is complicated, one soldering step can only perform part of the soldering job; so during manufacturing, it is not only necessary to enter vacuum and heating furnace many times for soldering, but the following problems also exist which cause the contact electrical properties to be not good enough: contact of the soldering surface is not 100%, quality of soldering surface and strength of soldering have not been guaranteed and burr on soldering surface is unavoidable etc. For reasons mentioned above, with current technology, production of vacuum interrupter not only has low ratio of final product, complicated procedure, these causing high cost, but does not have ideal electrical properties either. In addition, all components need various professional forms of copper-chromium alloy materials and machining work, such as lathing and milling, of the alloy materials is complicated.
There is another product, developed by HOLEC Co., Netherlands, with current technology, its magnetic field generating component 13 discards the original coil form and substitutes it with a set of electrical iron sheets 13, which is piled on CuCr arc proof component 11 of contact body and is fasten with rivet 14. Electrical iron sheets 13 have different sizes of break 131, 132 and 133, magnetic field is produced by induced current in the electrical iron sheets, and its concrete structures are shown in FIG. 3 and FIG. 4. The piled electrical iron sheets 13 on CuCr arc proof component 11 form a ladder-shape, when it is seen from front view; this not only simplifies the original contacts structure, but also increases the magnetic field intensity greatly. Even with this structure, the soldering method must be used in order to combine the separated conductive component 12 and electrical iron sheet 13 together. As machining methods of the structure are unchanged basically, so its cost and quality still have quite a few problems. In addition, as electrical iron sheets 13 are piled in plane, according to the right-handed screw law, when magnetic induce reaches the break of sheets and goes up layer by layer to form an axial magnetic flux, so the magnetic resistance is comparatively high. Furthermore, as the sheets 13 are piled in a ladder-shaped form, the heat conductive body is an eccentric body; this asymmetrical heat conductive body makes instant heat diffusion effect badly; which not only influences contact interrupting capability, but also makes the whole structure deform easily.
No matter which form is used, a very important point for the current contact structure is that, without any exception, every component of it is separately made. Therefore, manufacturing procedures are various, the quality is unstable and the properties are not good enough. This is just like the separated electronic elements in the early days, to implement an electrical function many separated elements needed to be soldered together. This not only increases working procedures and size, but also decreases reliability and properties.
In addition to increasing costs by the complicated structure and manufacturing procedures described above, the current technology used to produce the contact wastes great quantities of contact materials. Either as shown in FIG. 2, the traditional structure, or as shown in FIG. 3 and FIG. 4, the improved structure, remaining leftover bits and pieces after manufacturing of the components cannot be rationally used. So, the cost of the vacuum interrupter is increased.
Another important point is that, with the current technology the axial magnetic field on the contact surface is not well distributed. At the same time, external stray magnetic fields influence interrupting capability of contacts. Especially for the contact of a high volume interrupter, its axial magnetic field is more concentrated on a local part and this leads to a worse interrupting capability under high volume current condition. This disadvantage is a big limitation for production of high volume vacuum interrupters. In practice, accompanying with electricity is widespread used, demand of high volume vacuum interrupter is increased rapidly; for example: an electric generator requires control of electrical currents greater than one hundred and twenty (120) kilo amps (kA), on a distributing line using a vacuum interrupter as an interrupting device.